EP3064262A1 - Filter medium, method for producing a filter medium and filter element with a filter medium - Google Patents

Abstract

A filter medium (1), comprising a first media layer (2) and a second media layer (3), which second media layer (3) in a direction of intended flow (6) of the filter medium (1) behind the first media layer (2) is arranged, the first media layer (2) is formed as a nanofiber layer with nanofibers and wherein the second media layer (3) is formed as a support layer with an average basis weight of more than 60 g / m 2, wherein the first media layer has a first region (4) on the inflow side and has a second region (5) downstream of the second medium layer, characterized in that the nanofibers of the first region (4) have a smaller average fiber diameter than the nanofibers of the second region ( 5).

Description

Technical area

The invention relates to a filter medium for filtering fluids, in particular for filtering liquids, as well as a filter element with such a filter medium and a method for producing such a filter medium, in particular for use as Erodierfilter.

State of the art

It is known to arrange nanofibers on a much coarser support layer. The application of fine fibers to a support layer serves to stabilize the fine fiber layer in the filtration operation but also during processing, especially when folding the nanofibers.

A layered structure is also used in the tuning of media for the requirements of depth filtration. These media are usually followed by finer fibers in the direction of flow on coarser fibers. This is intended to achieve a fractionated separation of the particles in the depth of the medium. The goal here is a uniform possible loading of the filter medium and thus the optimal utilization of the pore volume available for the particle storage in the filter medium. The EP 2 222 385 A2 discloses, for example, nanofiber layer with a gradient in fiber diameter. However, this decreases in the flow direction.

In addition, erosion filter elements with filter media made of nonwoven fabric are already out of the EP 1 764 144 A1 to which reference is made with respect to the structure of an erosion filter in the context of the present invention. The structure of the filter medium used has a nanofiber layer which is applied to a cellulose support layer.

Disclosure of the invention

The object of the present invention is, starting from the EP 1 764 144 A1 to provide a foldable filter medium having at least one nanofiber layer which has better resistance.

The above object is achieved by a filter medium according to the invention having the features of claim 1.

A filter medium according to the invention comprises a first media layer and a second media layer, which second media layer is arranged behind the first media layer in a designated flow direction of the filter medium, wherein the first media layer is formed as a nanofiber layer with nanofibers and wherein the second media layer as a support layer with a average basis weight of more than 60 g / m ^{2 is} formed.

The first media layer of the filter medium according to the invention has a first region on the inflow side and a second region on the outflow side toward the second medium layer. The nanofibers of the first region have a smaller average fiber diameter than the nanofibers of the second region.

On the one hand, the filter medium according to the invention has an outstanding filter effect with comparatively low pressure loss and, despite the use of very fine nanofibers, is resistant to mechanical influence and chemically aggressive substances.

Advantageous embodiments of the invention are the subject of the dependent claims.

For a particularly good filter effect, it is advisable to use in the first region a particularly high number of nanofibers with smaller fiber diameters. Therefore, it is advantageous if more than 75% of the nanofibers of the first region have a smaller fiber diameter than the nanofibers of the second region.

There are known filter media, for example from the EP 2 398 633 A1 which are constructed in multiple layers and which have loosely arranged nanofibers between the layers. However, these nanofibers can increasingly mix after prolonged use, so that the gradient structure of the nanofiber layer is gradually lost. Therefore, it is advantageous if the nanofibers of the first region are deposited on the nanofibers of the second region, in particular by means of an electrospinning process. The nanofibers of the first region adhere predominantly to the nanofibers of the second region, predominantly through mold closure and / or surface interactions. Preferably also an additional adhesion the nanofibers of the first region as well as of the second region by an adhesion promoter which is located on the second medium layer, take place. This creates a beneficial additional reinforcement of adhesion.

The first region may consist of nanofibers having a mean fiber diameter of 50 to 400 nm, preferably 50 to 250 nm, more preferably 50 to 150 nm. These very fine nanofibers enable optimal filter behavior. The nanofibers of the first region are preferably produced in the electrospinning process.

The second region may consist of nanofibers with a mean fiber diameter of 150 to 1000 nm, preferably 150 to 500 nm, particularly preferably 150 to 299 nm. These rather coarser nanofibers support the nanofibers of the first region, increase the resistance of the fibers of the first region, and aid in filtering the fluid to be filtered. Nanofibers of the second region are preferably produced in the electrospinning process. Compared to fiber composites from other manufacturing processes, for example compared to spunbonded nonwovens, the electrospinning process can have advantages in that, in particular, smaller fiber diameters, thinner design of effective layers and lower scattering within the fiber layer with respect to fiber diameter or pore sizes are made possible.

The nanofibers of the first and / or the second region are particularly preferably one-component nanofibers. These are easier and processable with more uniform properties to a filter medium such as bicomponent and / or split fibers.

All nanofibers of the first media layer are particularly preferably produced by the electrospinning method.

Particularly preferably, the nanofibers of the first and / or the second region are arranged one above the other like a spider web. More preferably, the nanofibers of the first and / or second region have a substantially round cross-section. This in particular allows somewhat more uniform properties, since a change in position of a single fiber, in particular a rotation, does not lead to a significant change in the cross section of the individual fiber transversely to the flow direction.

The nanofibers of the first material layer may preferably consist of more than 75% of polyamide nanofibers, in particular 100% of polyamide. Nanofibers made of polyamide are time efficient and inexpensive to produce.

The first material layer preferably has a basis weight of less than 20 g / m ² , preferably less than 10 g / m ² , more preferably less than 1 g / m ² . Thus, for example, a high separation efficiency with the lowest possible pressure loss, sufficient overall stability and low material costs are achieved.

Further preferred nanofiber materials according to the present invention or materials which can be spun into nanofibers according to the present invention are polyolefins, polyacetals, polyesters, cellulose esters, cellulose ethers, polyalkylene sulfides, polyarylene oxides, polysulfones, modified polysulfones and / or mixtures of these polymers. Particularly preferred materials of the aforementioned classes of polymers which are suitable for the abovementioned nanofibers are in particular polyethylene, polypropylene, polyvinyl chloride, polymethyl methacrylate (and other acrylic resins), polystyrenes and / or copolymers of the abovementioned polymers comprising block copolymers of the type ABBA, and also polyvinylidene fluoride, polyvinylidene chloride , Polyvinyl alcohol in various degrees of hydrolysis (87% to 99.5%) in crosslinked or uncrosslinked form.

The mean fiber diameter of the nanofibers increases at least by a factor of 1.5 to 5.0 from the first to the second region; but preferably at least by a factor of 1.5 to 3.0. This refers to the total number of fibers in the first and in the second range. Of course, individual fibers in the first region may also be thinner than in the second region. However, on average over all fibers located in the first region, the fiber diameter increases by the aforementioned factor compared to all the fibers in the second region.

The second material layer, ie the support layer, can advantageously be configured as a meltblown or spunbond layer, or as a meltblown or spunbonded layer. These fiber webs have proven to filter fluids, especially liquids. In this case, the second material layer may consist of at least 50%, in particular at least 75% of the fibers of the second material layer of a polyester and / or a polypropylene. Alternatively, the second material layer may be formed as a cellulose-based layer.

The second material layer ideally consists of particularly resistant fibers. The fibers of this material layer can therefore advantageously have an average fiber diameter of more than 3 μm.

A filter element according to the invention has a filter medium according to the invention, wherein the filter medium of the filter element is folded.

This may particularly preferably be formed into a round body and wherein the filter element has two end disks, between which the round body formed from the filter medium is arranged, in particular edged. Of course, the filter element may also contain other components, e.g. have a cylindrical support body as a plastic molding or metal.

Particularly preferably, the round body may be formed star-shaped. Alternatively, the round body in the form according to the DE 10 2009 057 438 B3 be formed, whose disclosure in terms of the shape and design of a filter element in the context of the present invention, reference is made in its entirety.

The filter element can be designed in particular as a filter cartridge and be used for filtering liquids, such as water, oil or fuel.

One particular use of the filter element is its use as an erosion filter in an EDM machine.

When used as erosion filter, the mean fiber diameter of the respective regions of the first material layer can be matched to the particle spectrum of the medium to be filtered. As a result, an optimal filter cake is formed, which prevents the blocking of the underlying fibers. When used according to the invention as an erosion filter, the filter element must also be able to withstand a higher mechanical load than with air filters.

Incidentally, the first media layer can consist of more than two regions with nanofibers. In this case, the average fiber diameter of the nanofibers of the regions preferably increases from region to region from the upstream side to the second material layer.

The invention further relates to a method for producing a filter medium, in particular a filter medium for liquid filtration, the medium comprising a first media layer and a second media layer, which second media layer can be arranged in an intended flow direction of the filter medium, in particular behind the first media layer, wherein the first media layer as a nanofiber layer is formed with nanofibers and wherein the second media layer is formed as a support layer with an average basis weight of more than 60 g / m ² , wherein the support layer is provided and the nanofiber layer is applied with at least a first region and a second region on the support layer with the second region oriented toward the second media layer and the nanofibers of the first region having a smaller average fiber diameter than the nanofibers of the second region. In this case, the first and / or the second region of the nanofibers is preferably produced in the electrospinning process.

Brief description of the drawings

Further advantages emerge from the following description of the drawing. In the drawings, embodiments of the invention are shown. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

They show by way of example:

Fig. 1

a schematic representation of a filter medium with two layers of material according to an embodiment of the invention; and

Fig. 2a, 2b

schematic representation of a preferred embodiment of a filter element as erosion filter.

Embodiments of the invention

The figures are merely examples and are not intended to be limiting.

In FIG. 1 an embodiment of a filter medium 1 according to the invention is shown. In the illustrated figure, this filter medium has two layers of material 2 and 3, the first of the two layers of material 2 being in an upper and a lower one Section 4, 5 divided. The filter medium can be used to filter a fluid. A preferred application is the use as a particle filter for the purification of liquids.

The term "filter medium" refers to a structure for filtering a fluid. In this case, a retentate is formed on or in the filter medium and a filtrate, the purified fluid. Particularly preferably, particles are filtered out as a retentate from the fluid through the filter medium and thus removed from the fluid. Depending on the design of the filter medium particles and other substances can be completely or only partially removed from the fluid to be filtered.

The filter medium may be provided as part of a filter element. The filter element may e.g. be a replaceable part in a machine or plant. Such an exchangeable part may e.g. be a filter cartridge. If a filter medium becomes entangled with retentate, the filter cartridge can be replaced without affecting the entire machine.

The two layers of material 2 and 3 of the filter medium 1 are arranged one above the other in the flow direction 6. On the inflow side 7 and / or outflow side 8 of the two material layers 2 and 3 of the filter medium 1 further material layers may be provided.

A further material layer on the arrival and / or downstream side 7, 8 can be, for example, a coarse-meshed network structure which additionally holds the material layers 2 and 3 together. Other material layers are conceivable.

A first material layer 2 is a nanofiber nonwoven. The term "nanofibers" includes fibers having a mean fiber diameter in a range between one nanometer and 1000 nanometers.

In a preferred embodiment, the fibers which form the first material layer 2 are more than 90% nanofibers. More preferably, more than 95%, especially 99%, of the fibers containing the material layer are nanofibers.

The first material layer 2 is the material layer of the two material layers 2 and 3, which is arranged on the inflow side 7. The first material layer 2 has nanofibers with different mean fiber diameters. While finer nanofibers, so Nanofibers with a smaller average fiber diameter, are to be found in the region of the upstream side 7 of the material layer 2, coarser nanofibers, so nanofibers with a larger average fiber diameter on the side of the material layer 2 are found, which is connected to the second material layer 3.

At least in the upper 10% of the total height of the first material layer 2, a first region 4 is arranged with fibers consisting of fine nanofibers with a mean fiber diameter of 50 to 400 nm, preferably 50 to 250 nm, more preferably 50 to 150 nm.

At least in the lower 10% of the total height of the first material layer 2, a second region 5 is arranged with fibers, which consist of coarse nanofibers with a mean fiber diameter of 150 to 1000 nm, preferably 150 to 500 nm.

The fibers of the first region 4 have a smaller average fiber diameter than the fibers of the second region 5. The average fiber diameter can be determined from an image section from above. In this case, the fiber diameter of all fibers located in the image section can be determined and an average of these fiber diameters can be determined. Particularly preferred is the average fiber diameter by the method according to the DE 10 2009 043 273 A1 determines which patent application is fully referenced in the context of the present invention.

The 4 and 5 nanofibers can be made by a meltblown or electrospinning process. For producers of equipment for the production of very fine fibers by meltblown or electrospinning process is the uniformity of the fibers produced an essential quality criterion. It is intended to enable the customer to reproducibly produce fibers with a diameter that is as precisely defined as possible with little scattering. For example, it is possible to produce nanofibers in a defined manner with the aforementioned average fiber diameters and to arrange them one above the other in layers. Thus, the first material layer 2 may also be formed in multiple layers with two or more partial layers, which are arranged, for example, loosely, that is, without cohesive connection, one above the other.

Alternatively, the nanofibers of the regions 4 and / or 5 can be advantageously realized by means of a wet-laying process.

In the arrangement of the partial layers, a transition region between the partial layers can occur, in which both coarse and fine nanofibers are arranged. The material layers thus merge into each other between the areas 4 and 5.

The structure of the first material layer 2 thus has a gradient structure with respect to the fiber diameter, in which the mean fiber diameter of the nanofibers in the flow direction 6 increases. A gradient of the fiber diameter in the sense of the present invention may mean both a uniform increase but preferably also an uneven, in particular stepwise, increase in the fiber diameter in the flow direction 6. This increase in average fiber diameter increases by a factor of 1.5-5.0 from the first to the second region, based on the total number of nanofibers in the first and second regions 4 and 5; preferably by a factor of 1.5-3.0.

The average basis weight of the first material layer 2 is preferably less than 1 g / m ² .

The nanofibers of the first material layer 2 can be made of different materials in the regions 4 and 5. In a particularly preferred embodiment of the invention, however, the nanofibers of the first material layer are all made of the same material. Particularly preferably, the nanofibers may be polyamide fibers.

Preferably, the nanofibers of the first material layer 2 can all be produced in an electrospinning process, so that the entire nanofiber layer can be realized by this production process.

During deposition, the nanofibers of the first region adhere to the nanofibers of the second region by form closure and / or surface interactions.

The connection of the first and the second material layers 2 and 3 can be chosen arbitrarily. Thus, the first material layer 2 may be deposited in a preferred embodiment only on the second material layer 3.

In an alternative preferred embodiment, an adhesion promoter 9 is arranged between the two material layers 2 and 3. In this variant, an additional adhesion of the nanofibers of the first region 4 in addition to the Nanofibers of the second region 5 by the bonding agent 9, which is located on the second medium layer 3, can be achieved. This creates a beneficial additional reinforcement of adhesion. As adhesion promoter 9 is a variety of substances in question. Preferred adhesion promoters may be acrylic- and / or polyurethane-based and applied in particular in dispersion form. These adhesion promoters are particularly preferred since they dry at comparatively low temperatures.

The nanofibers of the first and second regions 4 and 5 are preferably deposited on each other like spider webs and can optionally be connected to the second material layer 3 by means of a bonding agent.

The second material layer 3 is a support layer made of a nonwoven fabric. This can e.g. be designed as a meltblown fiber fleece or a spunbond fiber fleece.

The average basis weight of the second material layer 3 may preferably be more than 60 g / m ² . The determination of the average basis weight is carried out according to DIN / EN ISO 536 for paper layers and according to DIN / EN 29073-1 for nonwovens.

The average basis weight of the support layer is thus at least 60 times greater than the average basis weight of the nanofiber nonwoven.

The mean fiber diameter of the fibers of the second material layer is more than 3 μm.

The fibers of the second material layer 3 may preferably be polyester and / or polypropylene fibers. Also cellulosic fibers can be preferably used for the second material layer.

The filter medium according to the invention can be used both for filtering gases and liquids. However, the use of the filter medium when used as a particulate filter in filtration of liquids brings particular advantages. In liquid filtration, due to the higher flow forces compared to gas filtration, special demands are placed on the stability of the filter media. Therefore, an increased mechanical stability is particularly needed here. Thin fine fiber overlays, such as nanofiber nets, can by themselves withstand these flow forces only when they are in a sufficiently thick layer. Since the pressure loss in the flow through a fiber bed with As the specific surface area and layer thickness of the fibers increase, thick and thus stable microfibers would have an uneconomically high pressure loss. Therefore, nanofibers are stabilized in each case by a carrier structure with comparatively coarse fibers.

The first media layer 2 can only be placed on the second media layer 3. However, the two media can also be glued together or welded to each other selectively or edge-sided. by ultrasonic welding.

Apart from the gradient construction with respect to the fiber diameter, the structure of the nanofiber layer can be adapted to the requirements of the filtration application and the carrier material. If the nanofiber layer is supported, for example, by a relatively open-pore spunbonded non-woven material as a second material layer 3, then the fiber layer in the lower region 5 of the nanofiber layer can be selected to be stronger than in the case of a meltblown nonwoven carrier.

Thick fibers are known to be mechanically and chemically more resistant than thin fibers. A major difficulty in the production of nanofiber media is to ensure sufficient stability of this fine fiber.

The arrangement of thicker nanofibers in the lower region 5 of the nanofiber layer, an increased resistance of this media layer 2 can be realized by an increased number of support points.

Due to the gradient buildup in the nanofiber layer, the second media layer 3 can be relatively coarse-pored and therefore cost-effective. The coating of the carrier or support layer with a nanofiber supporting layer and the Feinstfaserauflage can be done by means of electrospinning in one pass.

FIGS. 2a and 2b show different variants of a filter element 10 with a pleated filter medium 1 according to the embodiment of the Fig. 1 , The filter medium 1 is pleated star-shaped folded into a round body, which is closed at both ends with a first 11 and a second end plate 12. These two end plates 11, 12 are used for receiving and fixing and for sealing the filter element 10 in a housing of a filter system. On the outer circumference of the round body of the filter medium 1 fold edges are to be seen, which are parallel to a longitudinal direction of the support layer of the filter medium 1, while a transverse direction the support layer is perpendicular thereto. The flow direction 13 of the filter element 10 with a fluid is radially inwardly into the round body of the filter medium 1 inwards, where the filtered fluid can then flow off axially through an outlet from the filter element 10 again. In such an exemplary embodiment, the filter element 10 can be used, for example, as an erosion filter in an erosion machine and be used to remove particles from a liquid, in particular from water or an aqueous solution.

The mass of the polymer material used per surface section for forming the nanofibers of the first region 4 of the first material layer 2 may preferably be from 20% to 5000% of the mass of the polymer material used to form the nanofibers of the second region 5 of the first material layer 2.

Claims (15)

Filter medium (1), comprising a first media layer (2) and a second media layer (3), which second media layer (3) in a direction of intended flow (6) of the filter medium (1) behind the first media layer (2) is arranged, wherein the first media layer (2) is formed as a nanofiber layer with nanofibers and wherein the second media layer (3) is formed as a support layer with an average basis weight of more than 60 g / m ² ,
wherein the first media layer has a first region (4) on the inflow side and has a second region (5) downstream of the second medium layer, characterized in that the nanofibers of the first region (4) have a smaller average fiber diameter than the nanofibers of the second region ( 5). Filter medium according to claim 1, characterized in that more than 75% of the nanofibers of the first region (4) have a smaller fiber diameter than the nanofibers of the second region (5). Filter medium according to claim 1 or 2, characterized in that the nanofibers of the first region (4) and / or the nanofibers of the second region (5) are deposited on each other, in particular by means of an electrospinning process. Filter medium according to one of the preceding claims, characterized in that the first region (4) consists of nanofibers with a mean fiber diameter of 50 to 400 nm, preferably 50 to 250 nm, more preferably 50 to 150 nm. Filter medium according to one of the preceding claims, characterized in that the second region (5) consists of nanofibers with a mean fiber diameter of 150 to 1000 nm, preferably 150 to 500 nm, particularly preferably 150 to 299 nm. Filter medium according to one of the preceding claims, characterized in that the mean fiber diameter of the nanofibers, based on the total number of fibers in the first and in the second region (4, 5), from the first to the second region by a factor of 1.5-5.0 ; preferably by a factor of 1.5-3.0; increases. Filter medium according to one of the preceding claims, characterized in that the nanofibers of the first media layer (2) are more than 75% polyamide nanofibers. Filter medium according to one of the preceding claims, characterized in that the first media layer (2) has a basis weight of less than 20 g / m ² , preferably less than 10 g / m ² , more preferably less than 1 g / m ² . Filter medium according to one of the preceding claims, characterized in that the second media layer (3) is designed as a meltblown layer or as a spunbond layer. Filter medium according to one of the preceding claims, characterized in that at least 50%, especially at least 75% of the fibers of the second media layer (3) made of a polyester and / or made of a polypropylene. Filter medium according to one of the preceding claims, characterized in that the mean fiber diameter of the fibers of the second media layer (3) is more than 3 μm. Filter element (10) with a filter medium (1) according to one of the preceding claims, characterized in that the filter medium (1) of the filter element is folded and in particular formed into a round body, wherein the filter element (10) has two end plates (11, 12) , between which arranged from the filter medium (1) round body arranged, in particular edged, is. Use of the filter element according to claim 12 or of the filter medium according to one of claims 1 to 11 for the filtration of liquids, for example for water, oil, fuel or for the dielectric of a spark erosion machine. A method for producing a filter medium, in particular a liquid filter medium, in particular according to one of claims 1 to 11, wherein a support layer is provided and a nanofiber layer having at least a first region and a second region is applied to the support layer, the second region towards the second medium layer is oriented and the nanofibers of the first region have a smaller average fiber diameter than the nanofibers of the second region. The method of claim 14, wherein the first and / or the second region of the nanofibers is produced in the electrospinning process.

Images